[0001] The present invention relates to the field of sound producing prosthetic devices
for use by laryngectomized patients.
[0002] Many devices have been suggested for providing speech capability to laryngectomized
patients. One approach involves the provision of a mechanical or electromechanical
device to create pitches or tones which are modulated to produce speech. In Richard
L. Goode's review entitled "Artificial Laryngeal Devices In Post-Laryngectomy Rehabilitation",
which appeared in The Laryngoscope. (pages 677-689, 1974), two basic types of artificial
larynges, transcervical and transoral larynges, are disclosed. Transcervical larynges
are electronic, hand-held, battery-powered, vibrating devices that are placed on the
neck to produce voice. While transcervical devices have experienced considerable commercial
success, they must be hand held on the neck while speaking, produce an "electronic"
type of speech, leak unwanted sound from the neck, need battery changes, and require
a place on the neck that will allow efficient transfer of sound vibrations. Transoral
laryngeal devices are electronic or pneumatic devices in which the sound enters the
mouth through a tube. While such units produce a loud sound and may be used in early
post-operative stages by patients with thick neck tissue who cannot use transcervical
devices, transoral devices are noticeable in use, require placement in the mouth,
and are prone to saliva blockages. Additionally, transoral devices may result in articulation
which is disturbed by the placement of the tube near the tongue and lips, this results
in speech which is less intelligible than that produced by transcervical devices.
[0003] The desirability of including all of the operative components of an artificial larynx
on an intraoral prothesis has long been recognized. See for example U.S. 2,862,209,
Col. 1, lines 61-64. Unfortunately, the art has heretofore failed to disclose any
complete intraoral device:
One early attempt at an "intraoral" device is the "Tait larynx". In 1974 Goode, supra.
described the Tait larynx, "no longer manufactured", as comprising an intraoral earphone
attached to a patient's denture or dental retainer, an external power source, external
oscillator and external on-off switch. In the Tait device a wire was passed from the
intraoral earphone to these external components. While the sound produced by the Tait
device is at least comparable to that produced by other transoral larynges, the presence
of a wire caning out of the user's mouth makes the Tait device unacceptable to most
laryngectomees. For a disclosure of a similar transoral device see U.S. Patent 2,862,209.
[0004] Pichler eliminated any need for transoral wiring by suggesting that a wireless induction
system could be used to transmit sound from a pocket oscillator driven primary coil
worn around the neck to an intraoral secondary coil associated with an intraoral earphone.
However, Pichler's device has apparently never been placed on the market. See Goode,
supra.
[0005] In an attempt to improve upon the Pichler device, Goode suggests that a miniature
pulse generator capable of being mounted on a denture or dental retainer can be used
to drive a small, waterproof, low impedence, modified insert earphone. Power is provided
to the pulse generator by a hand-held, external radio frequency generator operating
at 100 kHz and using a 15-volt rechargeable battery pack, carried in the pocket, with
a battery drain of 780 mW. When the transmitter is held to the cheek, the transmitter
coil lies about 1.5 cm from a miniature, tuned receiving coil in the denture.
[0006] A wireless electro-larynx consisting of a receiver/ speaker concealed in an ordinary
denture or prosthesis, and an external transmitter worn under the patient's clothing
has been suggested by Zwitman et al. See "Development and Testing of an Intraoral
Electrolarynx for Laryngectomy Patients", Zwitman et al, Journal Of Speech And Hearing
Disorders, XLIII, 263-269 (May, 197B). In the Zwitman et al device, a 1 millimeter
thick receiver is housed in the center of the denture and surrounded by a receiving
coil which is used to pick up an incoming differentiated transmitter-generated pulse
which is then amplified. This amplified signal is used to change the state of a bistable
multivibrator circuit, which then activates an astable multivibrator. This astable
multivibrator then begins to oscillate at a repetition rate (fundamental frequency)
of 70 Hz to produce an audible buzz. Current is permitted to pass through the receiver
for only 0.3 msec periods, which are long enough to facilitate the generation of intelligible
speech, while conserving battery life. A plastic tube is attached to the speaker of
the Zwitman et al device which extends medially and slightly upward past the mid-line
of the palate to a point just short of the opposite side of the dental prosthesis.
This tube is intended to transmit sounds to the posterior region of the oral cavity
to provide maximum resonance, and to prevent the tongue from occluding the speaker
aperature. Two rechargable batteries are used to power the receiver/speaker for up
to five continuous hours. Since the standby current drain is low, Zwitman et al reported
that intermittent use of the unit permits it to function for an entire 1aay before
recharging is necessary.
[0007] In "A Modified Intraoral Electro-larynx", McRae et al, Archives of Otolaryngology
105: 360-361, 1979, and in "The Design of a Wireless-Controlled Intraoral Electro-larynx",
Knorr et al, Journal of Bioengineering 1: 165-171, 1977, other designs of intraoral
electro-larynges are disclosed.
[0008] More recently, in work conducted by Mr. Kenneth Stern, a self-contained, intra-oral
artificial larynx has been suggested, and Stern's described circuitry breadboarded.
This circuit generates a squarewave of 125 Hz which is used as a clock for a five
stage binary counter. Outputs of the counter are logically interconnected through
exclusive-or's, amplified, and used to energize a speaker to produce a buzz. By using
bi-lateral switches, most of the circuitry is not powered in order to extend battery
life.
[0009] Stern has suggested the desirability of providing a tongue operated switch for power
control, and of providing a speaker housed in the mouth which produces varied output
frequencies which simulate changes of pitch; however Stern has failed to provide designs
for these components.
[0010] As seen from the above, the desirability of providing a completely self-contained,
intraoral artificial larynx has long been recognized. Nonetheless, there is a long
felt need for a simple, intraoral, tongue-controlled larynx which may function without
recharging over extended periods of time, and which facilitates the generation of
clearly audible speech.
[0011] The present invention provides a novel, completely self-contained intraoral artificial
larynx. This larynx is an ultra thin, miniature device which may be mounted on or
within a dental appliance and is wholly contained in the mouth. Based on an estimate
of 3 hours per day of continuous speaking, the larynx of the present invention may
be used for up to 30 days without battery replacement or recharging.
[0012] The preferred embodiment of the present invention comprises a power source, tongue
activated controls, power saving signal generation circuitry, an audio amplifier,
an intraoral sound source, and an acoustic amplifier which is tuned to the output
of that speaker. Power saving signal generation circuitry is designed to produce a
high amplitude signal which drives the speaker to produce an "audio flicker". In the
preferred embodiment, the tongue activated controls comprise contacts located on the
palate which may be touched by the tongue to activate, deactivate, or temporarily
disable the artificial larynx. In order to prevent accidental activation or deactivation,
the on-off contact must be touched for preselected periods of time to produce the
desired activation or deactivation of the device. Occlusion of the speaker with saliva
or water is prevented by locating the speaker at one end of an acoustic horn, encapsulating
the speaker, and by disposing a liquid barrier means, such as a microporous film or
screen, over the speaker and/or horn orifice to prevent fouling of the speaker )with
mouth fluids. This barrier means is installed such that its attenuation of sound is
minimized.
[0013] Laryngectomized patients require short term training to use the device of the present
invention, and this device can be conveniently worn for extended periods of time.
Unlike prior art devices which have relied upon extra-oral components, the device
of the present invention is worn entirely within the mouth and is incapable of visual
detection. A unique combination of tongue controls for permitting convenient intermitent
use, novel power saving circuitry, and tuned acoustic amplification permit the device
of the present invention to be used for far longer periods between battery replacement
or recharge then has heretofore been possible.
[0014] In an alternate embodiment of the present invention, the artificial larynx is completely
sealed, and includes a solar cell for recharging a self-contained power source, such
as a rechargable battery. In this embodiment, the larynx is made so that the power
source may be recharged by placing it under a light source when it is not being worn.
[0015] In other alternate embodiments the circuitry of the preferred embodiment is simplified,
sound output is maximized, and current leakage and acoustic hum are minimized.
[0016] Accordingly, a primary object of the present invention is the provision of an entirely
self-contained, intraoral larynx.
[0017] A further object of the present invention is the provision of an intraoral larynx
which is entirely tongue controlled.
[0018] A further object of the present invention is the provision of a tongue controlled
intraoral switching device.
[0019] Another aim of the present invention is the provision of power saving signal generation
circuitry for use in driving an artificial larynx.
[0020] A further object of the present invention is the provision of an artificial larynx
which resists fouling by saliva or water.
[0021] A further aim of the pres nt invention is the provision of an artificial larynx having
a tuned acoustic amplifier for maximizing the amplitude of sound generated by the
electronic tone generator.
[0022] These and further objects of the present invention will become apparent from the
following, more detailed description.
[0023]
Fig. 1 is a diagramatic plan view of the top surface of a preferred embodiment artificial
larynx, diagramatically illustrating the speaker, battery, solar cell, acoustic horn,
mesh and tongue contacts which are contained within an otherwise conventional dental
prosthesis;
Fig. 2 is a block diagram illustrating the operative components of the preferred embodiment
artificial larynx of the present invention, an alternative embodiment being illustrated
with dotted lines;
Fig. 3 is a circuit diagram of the preferred embodiment represented in Fig. 2;
Fig. 4 is an enlarged cross-section of the terminal portion of an alternate embodiment
horn over which is diposed a microporous barrier; and
Fig. 5 is a circuit diagram of an alternate amplifier circuit.
[0024] While specific forms of the present invention have been selected for the purposes
of illustration, one of ordinary skill in the art will recognize that various departures
may be made to the examples set forth herein without departing from the scope of the
present invention, which is defined more particularly in the appended claims.
[0025] The intraoral artificial larynx of the present invention generally comprises a prosthetic
means for mounting the larynx within the oral cavity, a power source mounted on the
prosthetic means, signal generation means mounted on the prosthetic means for generating
preselected electrical signals, and speaker means mounted on the prosthetic means
for converting said signal into acoustic energy. Referring now to Fig. 1, the prosthetic
means, designated generally 100, will be seen to generally comprise a conventional
palatal denture or dental prosthesis. Such a prosthesis usually comprises means for
anchoring the prosthesis in the mouth cavity, such means in Fig. 1 being dental wires
102, 104 and 106. The body 108 of the dental prosthesis is formed from conventional
dental prosthetic materials, such as an acrylic polymer, which is shaped to fit comfortably
against the roof of the wearer's mouth. This body is preferrably formed to encapsulate
all of the electrical components of the preferred embodiment larynx, and is molded
to contain an acoustic horn 110, which is the preferred acoustic amplification means
for amplifying acoustic energy generated by the aforementioned speaker means. As shown
in Fig. 1, the preferred acoustic horn 110 is arcuate, having its minimum diameter
at its juncture with speaker 112 and its maximum diameter at its terminus 110a at
the rear of the dental prosthesis 100. In order to maximize achieved amplification,
horn 110 is generally circular at its point of coupling to speaker 112 and gradually
becomes elliptical as it approaches its terminus 110a.
[0026] In the embodiment illustrated in Figure 1, a gentle curvature of the horn has been
selected. Alternatively the horn may double back on itself so that this component
is located entirely on one side of the mid-line of the prosthesis. In this instance
a metal (stainless steel) spiral or spring may be used in the bend of the horn to
maintain the (1/8") lumen of the horn.
[0027] In forming the horn for this alternate embodiment, a length of heat settable 1/8"
I.D. tubing (available from Chemotron, Inc.) may be formed into its desired shape
using a (silicone coated) conical jig inserted into one end of the tube and a speaker
form jig into the other. With the stainless steel spring disposed at the point of
bend, the horn may be bent over on itself, fastened or wrapped in that position, and
heat set, as for example through immersion in boiling water. Once set, the jigs may
be removed from the horn and the speaker or speakers fitted into the proximal end
of the horn. If desired, the terminal end of the horn may have been sealed with a
barrier means as described hereinafter. Additional liquid tight seals between these
and/or other components may be provided by dipping them into an air dry solution of
trichlorethane. Such a solution is commercially available under the trade name "Dip
It" from Plasti-Dip International, of St. Paul, Minnesota, 55113.
[0028] The length of acoustic horn 110 is carefully selected to maximize the audible output
of tones generated by speaker 112. A tuning process, an example of Which is described
more fully hereinafter, should thus be performed which includes testing the desired
circuitry with acoustic horns of varying lengths and configurations until maximum
amplitudes are achieved for given frequencies. For the preferred embodiment for the
present invention, horn 110 should have an acoustic length of between about 1.50 and
2.75 inches, preferably about 1.75 and 2.25 inches.
[0029] The larynx of the present invention is controlled by bridging anterior contacts 114,
or posterior contacts l16 with the tongue. As is described more fully hereinafter,
the touching of either of these pairs contacts acts to complete a ground path in the
artificial larynx. Anterior contacts 114 provide a pause control which instantaneously
interrupts the generation of sound by the larynx for as long as the contacts are bridged.
The posterior contacts 116 provide an on-off control which must be touched by the
tongue for a pre-selected period of time. By requiring prolonged tongue contact of
posterior contacts 116, inadvertant switching between the off and on positions is
effectively prevented.
[0030] In an alternate embodiment, the grounding contact of each pair of contacts may be
common to the pause and off-on switches. Accordingly, only three adjacent contacts
are needed in this embodiment. These contacts can then be conveniently placed at the
anterior of the prosthesis with the grounding contact located between the on-off and
pause contacts.
[0031] The efficiency of the sound circuitry makes it possible to use a low-voltage, low-current
power source, such as batteries 118. For the embodiment shown in Fig. 1, these batteries
may be entirely sealed within the dental prosthesis 100, and may be of the lithium,
silver oxide, or nickel cadium type. In alternate embodiments replacement of such
batteries may be permitted. It is presently preferred to provide a solar cell 120
which is located within the dental prosthesis adjacent to an area of transparent material
in that prosthesis. The current drain of the larynx of the present invention is sufficiently
low as to facilitate recharging of the larynx on a periodic basis by removing the
larynx and replacing it under an artificial light source, such as incandescent light.
[0032] Special precautions are taken to prevent speaker 112 from becoming fouled with water
or saliva. In addition to increasing the amplitude of sound generated by speaker 112,
acoustic horn 110 aids in protecting speaker l12 from liquids contained within the
mouth. This protection results from the location of the speaker at the proximate end
of the horn, and may be further enhanced through the provision of a mesh 122 located
at the speaker orifice. Applicants have found that introduction of saliva or water
into acoustic horn 110 is unlikely, and that such amounts as may be introduced to
acoustic horn 110 are generally shielded from speaker l12 by mesh 122. Mesh 122 does
not appreciably interfere with sound transmission from the speaker 112 to horn 110.
[0033] Additional protection against flooding may be attained by covering the mouth of the
horn 110 with a thin sheet of material which will prevent liquids from entering the
horn but Which will permit water vapor and air to pass therethrough. Hydrophobic microporous
materials such as polytetrafluoroethylene sheets (half mil) sold under the tradename
"Teflon® FEP fluorocarbon film" by American Durafilm Co, Inc. of Newton Lower Falls,
MA, are suitable for this purpose.
[0034] Use of a microporous cover over horn 110 will, however, cause some attenuation of
sound. This attenuation can be minimized to about 4dB or less if care is taken to
install the sheet as illustrate in figure 4. In this Figure, the sheet 111 is shown
wrapped over the end 110a of the horn and bound to an outer circumferential surface
of that end using a binding, such as suture thread 113, to create a liquid tight seal
with the horn. The portion of the sheet 111 disposed over the mouth of 'the horn is
loosely draped into the horn mouth such that it extends from between about 1/4" to
1/8" into the mouth of the horn. This loose drape of the sheet material is sufficient
to prevent sound attenuation, but not so great as to facilitate entrapment of liquids
in the horn orifice. This microporous sheet, when used as described above, may supplement
or replace the aforementioned mesh.
[0035] Fig. 1 diagrammatically illustrates representative mountings of solar cell 120, battery
118, sound generation circuitry 124, speaker 112, mesh 122, contacts 114 and 116,
and acoustic horn 110. Fig. 2 provides further information concerning the operation
of the preferred embodiment larynx of the present invention. In Figure 2, further
details of the sound generation and switching circuitry are provided. As a matter
of illustrative convenience, batteries 118 and solar cell 120 are not illustrated
in Figures 2 or 3. Figure 3 is a circuit diagram providing the details of the circuit
which is diagrammatically illustrated in Figure 2. Portions of the circuit illustrated
in Figure 3 which correspond to blocks illustrated in Figure 2 are surrounded by similarly
numbered dotted outlines.
[0036] Referring now to Figures 2 and 3, the signal generation circuitry of the present
invention is seen to comprise a signal generator 200 and differentiator 202. In the
preferred embodiment, a square wave signal generator is utilized, the resultant signal
of which is differentiated to produce an output signal comprising a plurality of spikes
which are separated by long near-zero voltage time periods. In the preferred embodiment,
the square wave signal generator comprises an astable multivibrator which generates
a signal having a frequency between 0 and 20 KHz preferably 60-120 Hz. By differentiating
the signal generator output, the frequency and maximum amplitudes of the positive
and negative spikes produced thereby will, of course, correspond to the frequency
and amplitude of the square wave signal. The periods of return to near-zero voltage
between spikes of the differentiated signal are too short to be audibly resolved,
and thus, an "audio flicker" is created when the output, signal is fed to audio amplifier
212, and to speaker 112 to produce the output tone of the larynx. Thus, the amplitude
and frequency of the apparent sound produced by the larynx has not been changed, while
the duty cycle, and thus the power drain, of the output signal has been substantially
reduced. A duty cycle control means is thus provided which is utilized to reduce the
duty cycle of the output of the signal generation means by profitably utilizing the
audio flicker effect. In the preferred embodiment, the duty cycle of the sound generation
means is at least less than 10%, generally less than 5%, and most preferably less
that about 1.0%. In fact, good results have been obtained using a duty cycle of about
0.85%.
[0037] The preferred embodiment artificial larynx further comprises a tongue activatable
intraoral switching device. This switching device comprises an on-off circuit for
activating or deactivating the device. This selective enabling and disabling function
is accomplished by providing a timing means for timing the closure of a switch which,
in the prefer- red embodiment, is accomplished by completion of a ground path through
contacts 116. The desired grounding may be accomplished by bridging between adjacent
contacts with the tongue, or by using the body as the system's ground whereby touching
a single contact will accomplish a grounding of the system. In this embodiment, counter
204 counts in response to the output (φ) of the signal generation means when the on-off
contacts 116 are grounded, but is inhibited (through Rll in Fig. 3) from counting
when the on-off contacts 116 are not grounded. In order to turn on the artificial
larynx, the tongue is held against "on-off" contacts 116 until counter 204 has been
permited to count for a preselected period of time, after which an output pulse is
provided to differentiator and inverter 206. The output pulse of counter 204 is thus
differentiated and inverted in 206 in order to provide a distinct output to bistable
multivibrator (flip-flop) device 208, which is caused to assume its "on" position.
When in this position, flip-flop 208 provides a high level signal to "and" gate 210.
If anterior "pause" contacts 114 are not grounded, and thus also provide a high level
signal to "and" gate 210, then the differentiated output of signal generator 200 will
be permitted to pass to high gain amplifier 212 and to speaker 112. When the user
hears the signal from speaker 112, the tongue may be removed from on-off contact 116,
and the flip-flop 208 will remain in its "on" position.
[0038] As mentioned above, pause contacts 114 are utilized to momentarily deactivate amplifier
212 and speaker 112. Under normal conditions, pause contacts 114 are open, and thus
the signal to "and" gate 210 is high (through Rl2 in Fig. 3), permitting, in canbination
with a high signal from flip-flop 208, the passage of the differentiated output signal
202 to amplifier 212 and speaker 112. When the tongue is used to bridge pause contacts
114, the output drops to zero, and "and" gate 210 prevents the transfer of any signal
to the amplifier and speaker.
[0039] It is anticipated that the switching device of the present invention may be utilized
by a proficient user to closely approximate natural speech. The pause contact 114
may be utilized to stop any sound from being generated between sentences, or even
between words.
[0040] In Fig. 3, a circuit diagram corresponding to the block diagram set forth in Fig.
2 is provided, each of the blocks of Fig. 2 being illustrated within dotted outlines
surrounding its respective circuit components. Preferred components for use in constructing
the preferred embodiment artificial larynx are as follows

[0041] One of ordinary skill in this art will readily appreciate that while certain signal
generator of frequencies have been selected for use in the disclosed artificial larynx,
other frequencies and/or dual frequencies may be provided to accomodate individual
preferences. Similarly, connections to pins Q7 and Q8 of binary counter IC2 provide
the aforementioned two second and four second on-off times. Other combinations of
connections Q1-Q14 may be used to speed, slow, or otherwise alter the relative on-off
times of the preferred embodiment device.
[0042] As mentioned above, it is preferred to provide an acoustic amplification means for
amplifying acoustic energy within the oral cavity. It is further desired to tune the
acoustic amplification means to the sound source to maximize the amplification. Accordingly,
tests have been conducted to demonstrate the effectiveness of a horn to amplify the
output of a speaker of the type preferred for use in the artificial larynx of the
present invention. In one set of tests, the output of a BK1610 speaker was fed into
a horn. The output from the horn was compared to the output of a similar BK1610 speaker,
sound measurements being taken using a Scott type 451 (A weighted) sound meter. At
80 Hz, the speaker with horn generated a 57 decibel tone, by comparison to a 51 decibel
tone generated by the speaker without a horn. At 120 Hz a 60 decibel output was achieved
with the horn and a 53 decibel output without the horn. At combined input frequencies
of 80 and 120 Hz, a 62 decibel output was achieved with the horn, and a 54 decibel
output achieved without the horn. These changes are quite significant. A 6 decibel
change indicates twice the pressure level, while a 10 decibel change indicates that
the sound is perceived as being twice as loud.
[0043] In order to further investigate the effect of different horn lengths, a study was
undertaken to determine the optimal length using a 1-1/2 volt circuit powering a BK1610
speaker. This speaker was placed at varying distances from the diaphram of a sound
level meter, to ascertain the optimal length for an acoustic horn. Ambient sound accounted
for 40 decibels under "no signal" conditions. Lengths of between 3/4 of an inch and
9-1/4 inches were tested, with maximum values of 98 decibels being obtained for 1-3/4
and 2 inch lengths. This testing is set forth in Table I :

[0044] Although the results set forth in Table I were obtained using a straight, cylindrical
horn, the above-described tests were repeated using an arcuate, elliptical horn, and
comparable results were obtained. It should further be noted that the circuitry used
to drive the speaker in the tests refered to above was early prototype circuitry which
failed to comprise any duty cycle control means.
[0045] One of ordinary skill in the art will appreciate that the voltage of the preferred
embodiment device may also be varied, and that with such variations, some variation
in loudness will be obtained. Using the preferred embodiment circuitry of the present
invention, it has been found that a decibel output of between about 91 and 111 decibels
may be obtained using different values for resistor R10 in section 212. Table II,
which is set forth below, provides information concerning current drain for both conditions
of 'device on' and 'device off' and the decibel output for different values of R10.

[0046] As seen from the above, depending upon the loudness and the current drain desired,
different values of amplifier resistor R10 may be provided to power the preferred
embodiment larynx of the present invention.
[0047] In alternate embodiments of the present invention modification may be made to the,
above-described circuitry. One such embodiment is represented by the dotted line in
Figure 2, which facilitates elimination of the "differentiate and invert" component
206. In this embodiment the outputs of counter 204 are each fed to an additional NAND
gate, which NAND gates also receive as inputs the output of differentiator 202. These
NAND gates in turn separately feed the inputs of flip-flop 208, thereby eliminating
the discrete components of the differentiate and invert block 206.
[0048] In a further alternate embodiment a filter capacitor is provided to eliminate perceived
hum' by the user when the device is in the of for pause condition. This filter capacitor
may simply by connected between the power source (+V) and ground, and acts to eliminate
any detectable "leak through" of the signal to the speaker while the unit is in the
off or pause condition. A 10 ufd capacitor has been found suitable for this purpose,
and may be mounted for removal with a replaceable or rechargable power source.
[0049] In still another embodiment of the present invention, the current passing to the
tongue may be reduced by increasing the resistor value of resistors Rll and R12 to
680 K, which reduces the current between contacts to less than 2 u amps during operation
of the contact switches.
[0050] Those of ordinary skill in this art will recognize that the oscillator period of
the signal generator 200 may be varied depending upon the value of resistor R2. For
example, periods of 17 msec, 8 msec, 10 msec and 8.8 msec may be obtained using R2
values of 680K, 270K, 390K and 330K respectively. Presently, oscillator periods of
between 10-17, preferably about 14, milliseconds are preferred by most patients.
[0051] Those of ordinary skill in this art will further recognize that the amplifier circuit
212 may be modified to achieve desired outputs at acceptable current draws. Both common
collector and common emitter amplifiers are believed to be operative in driving the
speaker means, however a common collector, direct coupled audio circuit (Figure 5)
comprising an NPN transistor (Amperex LDA-404), a silicon flyback diode (Amperex LDD-5)
across the speaker terminals and a 1.5 ufd capacitor across the battery connections,
is currently preferred. The flyback diode provides a cleaner signal at a lower current
drain, while the capacitor enables the battery to supply the required current pulse
to the speaker. Without this capacitor, the volume is substantially reduced.
[0052] Using 'the above described direct coupled audio circuit, a 14 millisecond oscillator
period, and a Fluke DVM8022A in series with a battery plus lead to measure the overall
current, the following results were obtained:

[0053] In accordance with one preferred embodiment, the speaker means of the present invention
should comprise two phased speakers, wired in parallel, connected to the output of
the amplifier 212. The use of two transducers, such as BK-1610's, BK-8212's or BK-1911's,
has been shown to result in increased audio outputs. The outputs of single vs. dual
speakers using common emitter (Type B) and common collector (Type A) (Figure 5) type
amplifier circuits were compared. The results are summarized below:

[0054] As seen from the above, the use of dual speakers may offset db losses Which may result
from using microporous barrier means over the horn orifice.
[0055] While discrete electronic components are described above, one of ordinary skill in
the art will readily appreciate that most of the disclosed circuit components can
be included in a single semiconductor chip, and that such a chip is preferred for
construction of the preferred embodiment of the present invention.
[0056] As seen from the above, a highly efficient wholly self contained artificial larynx
is described which overcomes many of the disadvantages of prior art devices.
1. An intraoral artificial larynx, comprising:
(a) prosthetic means for mounting said larynx within the oral cavity;
(b) a power source mounted on said prosthetic means;
(c) signal generation means mounted on said prosthetic means for generating a preselected
electrical signal; and
(d) speaker means mounted on said prosthetic means for converting said signal into
acoustic energy;
(e) duty cycle control means for reducing the duty cycle of said signal prior to its
input to said speaker means to produce a conditioned signal;
(f) a tongue activatable switch;
(g) switched timing means for enabling said speaker means in response to a timed closure
of said switch, said switched timing means comprising a timer and a bistable flip-flop
responsive through NAND gates to the output of said timer and one of said signals.
2. The larynx of claim 1 wherein said signal is said conditioned signal.
3. An intraoral artificial larynx, comprising:
(a) prosthetic means for mounting said larynx within the oral cavity;
(b) a power source mounted on said prosthetic means;
(c) signal generation means mounted on said prosthetic means for generating a preselected
electrical signal;
(d) speaker means mounted on said prosthetic means for converting said signal into
acoustic energy;
(e) switching means for selectively disabling said speaker means; and
(f) filter capacitor means for coupling said power source to ground to reduce leakage
of said signal to said speaker means when said switching means has disabled said speaker.
4. An intraoral artifical larynx, comprising:
(a) prosthetic means for mounting said larynx within the oral cavity;
(b) a power source mounted on said prosthetic means; J
(c) signal generation means mounted on said prosthetic means for generating a preselected
electrical signal;
(d) speaker means mounted on said prosthetic means for converting said signal into
acoustic energy; and
(e) liquid barrier means for protecting said speaker means from flooding with saliva.
5. The larynx of claim 4 wherein said barrier means is a porous sheet which permits
sound to pass but blocks saliva from passing therethrough.
6. The larynx of claim 5 wherein said barrier means comprises a mesh sheet.
7. The larynx of claim 5 wherein said barrier means comprises an acoustic horn connected
to said speaker means.
8. The larynx of claim 7 wherein said barrier means comprises a sheet disposed over
the end of said horn which is liquid sealed with respect to a circumferential outer
surface of said horn.
9. The larynx of claim 8 wherein said sheet extends into a portion of the interior
of said horn.
10. The larynx of claim 8 wherein said sheet is liquid sealed by binding said sheet
to said outer surface of said horn.
11. An intraoral artifical larynx, comprising:
(a) prosthetic means for mounting said larynx within the oral vacity;
(b) a power source mounted on said prosthetic means;
(c) a signal generation means mounted on said prosthetic means for generating a preselected
electrical signal;
(d) speaker means mounted on said prosthetic means for converting said signal into
acoustic energy; and
(e) amplification means for amplifying said signal comprising a common collector amplifier,
and a flyback diode connected across the inputs of said speaker means.
12. The larynx of claim 11, wherein said power source further comprises a battery
and a capacitor connected across the leads of said battery, which in combination are
sufficient to satisfy the power pulse requirements of said speaker means when driven
to optimal amplitudes.
13. An intraoral artificial larynx, comprising:
(a) prosthetic means for mounting said larynx within the oral cavity;
(b) a power source mounted on said prosthetic means;
(c) signal generation means mounted on said prosthetic means for generating a preselected
electrical signal; and
(d) speaker means mounted on said prosthetic means for converting said signal into
acoustic energy;
said speaker means comprising a plurality of phased speakers.
14. The larynx of claim 13, wherein said speakers are connected in parallel.
15. The larynx of claim 13, wherein said speaker means comprises an acoustic horn
which receives and amplifies the acoustic outputs of said plurality of speakers.